There is known a plasma treatment step which applies plasma to a processing object such as a substrate, in manufacturing a semiconductor device, a liquid crystal panel, a disk, or the like, or in a sputtering process, and the like. In this plasma treatment step, a direct current (DC) power source supplies a plasma generator with DC power, thereby allowing processed gas to be plasmatized, or the like, in the space within the plasma generator, so as to generate plasma, and using thus generated plasma, a film forming process or an etching process is performed on a surface of the substrate.
Typically, the plasma generator corresponds to an electrical load when viewed from the DC power source, and the load at a starting point for generating a plasma discharge before the plasma discharge is actually generated, is different from the load during a normal operation when the plasma discharge is generated stably. Therefore, usually, upon starting the plasma discharge, the DC power source applies ignition voltage which is higher than the voltage for the normal operation, for a certain period of time, and thereafter applies low discharge voltage during the period of the normal operation (Patent Document 1). In addition, it is known that starting of the plasma discharge is detected by incoming current (Patent Documents 2 and 3).
As a circuit for generating the ignition voltage for the plasma discharge generation, there is known a circuit using a resonant converter or a circuit using chopper control.
FIG. 13A and FIG. 13B each illustrates an ignition voltage generation circuit using the resonant converter; FIG. 13A illustrates a circuit example of a series resonant converter, and FIG. 13B illustrates a circuit example of a parallel resonant converter. In the circuit example as shown in FIG. 13A, the series resonant circuit LC is connected between an inverter circuit and a converter made up of a diode rectifier circuit, and in the circuit example as shown in FIG. 13B, the parallel resonant circuit LC is connected between the inverter circuit and the converter made up of the diode rectifier circuit. The ignition voltage generation circuit using the resonant converter boosts the ignition voltage by resonance.
FIG. 13C is a circuit example of the chopper control, and a chopper circuit is provided between a DC source (Ein) and the inverter circuit. In the circuit for the chopper control, the ignition voltage is controlled by an on-duty cycle of a switching element provided in the chopper circuit.